To determine the protective effect of Youmans' ribosomal vaccine in guinea pigs by utilizing an experimental design divided into 6 groups of 40 conditioned guinea pigs. Six weeks avter vaccination, 20 animals from each group will be challenged by aerosol with 50-100 viable units of M. tuberculosis, Erdman strain of known high virulence. The remaining 20 animals of each group will be challenged intraperitoneally with 1,000 v.u. of the same organism. The course of the infection will be followed by weighing the animals frequently and recording the survival time. Infected animals surviving 36 weeks will be sacrificed and necropsied. An additional group of 20 guinea pigs will be used to test for the development of delayed type hypersensitivity after vaccination.